श्री भगवानुवाच सुदुर्दर्शमिदं रूपं दृष्टवानसि यन्मम। देवा अप्यस्य रूपस्य नित्यं दर्शनकाङ्क्षिणः ॥

su-durdarśham idaṁ rūpaṁ dṛiṣhṭavān asi yan mama devā apy asya rūpasya nityaṁ darśhana-kāṅkṣhiṇaḥ

This Form of Mine beholden by thee is very hard to see. Verily the Shining Ones ever long to behold this form.

In plain words: Krishna says the form Arjuna saw is very hard to see. Even the gods always long to see it.